1. Technical Field
The present invention relates to an optical filter device, an optical module, and an electronic apparatus.
2. Related Art
Traditionally, a variable-wavelength interference filter in which reflection films are arranged to face each other via a predetermined gap, on surfaces facing each other of a pair of substrates, is known. Also, an optical filter device having such a variable-wavelength interference filter housed in a casing is known (see, for example, JP-A-2008-70163).
The optical filter device disclosed in JP-A-2008-70163 has a package (casing) that includes a plate-like pedestal (base substrate) and a cylindrical cap. In this casing, a peripheral edge portion of the base substrate and one end portion of the cylinder of the cap are welded or bonded and thus connected together, and a space for housing the variable-wavelength interference filter is provided between the base substrate and the cap. A hole is provided in a top surface of the cap that is opposite to the pedestal, and a window portion for transmitting light is provided in this hole.
By the way, a light transmission hole may be provided not only in the cap as in JP-A-2008-70163 but also in the base substrate. However, parallelism of the base substrate may be impaired in the processing to form the light transmission hole or the like. For example, a curvature, protrusion or the like is generated near an outer peripheral edge of the light transmission hole. If the base substrate with the impaired parallelism and the variable-wavelength interference filter are joined together, the curving part or protruding part locally contacts the joining surface of the variable-wavelength interference filter and therefore prevents horizontal fixture of the variable-wavelength interference filter. Consequently, there is a problem that resolution is lowered.